Blood cells are responsible for the defense system in the body. like red blood cells, these cells are formed from the stem cells of the . the different types of these cells have life spans from hours to . approximately 5 to 10 of these cells are found per microliter of blood. their function includes defense of the body against infection. these cells use the process of to leave the circulation and move toward areas of infection or inflammation. they move about within the interstitial fluid by the process of motion.